1. Field of the Invention
The present invention relates to a method for adjusting white balance and device thereof, especially to a method for adjusting white balance in an FSD and device thereof.
2. Description of the Prior Art
The methods for color mixture while displaying images on a display can be divided into two categories: a time method and a spatial method. The time method for color mixture utilizes different time axes for the three primary light sources, RGB (red, green, and blue), to pass through, such as the color concurrent method and the color sequential method. Both methods utilize the photogene phenomenon of the human eyes to sense the color-mixing result. The spatial method for color mixture is, for example, the strip alignment method. Take the TFT-LCD (Thin Field Transistor Liquid Crystal Display) as an example, applied with the strip alignment method, each pixel in the TFT-LCD is composed of RGB sub-pixels filtered by the color filter, and each sub-pixel is smaller than the angle of view that a person can sense. Therefore, when a person watches the TFT-LCD panel, he senses the color-mixing result generated by the RGB lights emitted from those RGB sub-pixels respectively. Please refer to FIG. 1. FIG. 1 is the diagram of the color concurrent method, the color sequential method, and the strip alignment method. So far the strip alignment method with a color filter is the main-stream of the color-mixing method applied in LCD panels; however, the color sequential method is gradually tending to catch up with the strip alignment method. Compared with the strip alignment method, the color sequential method has advantages of:
1. high resolution;
2. capable of performing color balance;
3. with no color filter.
With the above advantages, the performance of the system is better, the size of the system can be decreased, and the structure of the cavity of liquid crystal is simplified. A display applied with the color sequential method is called a field sequential liquid crystal display (FS-LCD).
Please refer to FIG. 2. FIG. 2 is a block diagram of conventional driving circuitry 10 of an FS-LCD. There are a video source 12 for offering video frequency signals, an FS-LCD controller 14, a memory 16, a display panel 18, and a backlight module 20 in the conventional driving circuitry 10 of FIG. 2. As shown in FIG. 2, the parallel RGB video frequency signals and the control signals are inputted from the video source 12 to the FS-LCD controller 14. The FS-LCD controller 14 further includes buffers F1 and F2, a converter 141, and a memory I/O 143. The buffer F1 is for receiving the video frequency signals transmitted from the video source 12, such as the parallel RGB video frequency signals and the control signals. The converter 141 is for converting the parallel RGB video frequency signals into the serial RGB video frequency signals. The buffer F2 is for outputting the serial RGB video frequency signals transmitted from the converter 141. The memory I/O 143 is for inputting/outputting the signals from/to the memory 16. After receiving the video frequency signals transmitted from the video source 12 by the buffer F1, the buffer F2 outputs the control signals to the backlight module 20 and the serial RGB video frequency signals converted from the parallel RGB video frequency signals by the converter 141 to the display panel 18. When the buffer F2 outputs the control signals to the backlight module 20, the FS-LCD controller 14 controls the backlight module 20 synchronously to light up corresponding light sources of the backlight module 20 according to the RGB signals intended to be shown on the display panel 18.
Please refer to FIG. 3. FIG. 3 is the schematic diagram of driving circuitry 200 of a backlight module 20 of a conventional FS-LCD. The driving circuitry 200 of the backlight module 20 includes a red LED (light emitting diode) series 202, a green LED series 204, a blue LED series 206, switches 212, 214, and 216, a DC power source 208, a ground source 210, and resistors 222, 224, and 226. The resistor 222 is electrically connected between the DC power source 208 and the red LED series 202, the resistor 224 is electrically connected between the DC power source 208 and the green LED series 204, and the resistor 226 is electrically connected between the DC power source 208 and the blue LED series 206. The switch 212 is electrically connected between the red LED series 202 and the ground source 210, the switch 214 is electrically connected between the green LED series 204 and the ground source 210, and the switch 216 is electrically connected between the blue LED series 206 and the ground source 210.
The driving circuitry 200 of the backlight module 20 lights up the LED series of different colors through controlling the corresponding switches 212, 214, and 216 according to different RGB signals intended to be shown on the display panel 18. Please refer to FIG. 4. FIG. 4 is the conventional driving wave form of the backlight module 20 of an FS-LCD. From FIG. 4, we can see that after a red part of an image signal is written into the driving circuitry 200 of the backlight module 20, the red LED series 202 of the backlight module 20 will be lighted up accordingly. Then a green part of the image signal is written into the driving circuitry 200 of the backlight module 20, and the green LED series 204 of the backlight module 20 will be lighted up accordingly. Lastly a blue part of the image signal is written into the driving circuitry 200 of the backlight module 20, and the blue LED series 206 of the backlight module 20 will be lighted up accordingly. As shown in FIG. 4, due to the fixed switch cycle of the LEDs, adjusting the luminance of the LEDs only can rely on adjusting the resistance values of the resistors 222, 224, and 226 in FIG. 3. In the prior art, the resistance values of the resistors 222, 224, and 226 are adjusted manually so as to control the currents flowing through the corresponding LEDs of the backlight module 20. However, the adjusted luminance of the LEDs can only be judged through human eyes, therefore the outcome of the judgment is not very precise; and moreover, it is difficult to fine tune the resistance values through a manual operation. As a result, a color shift will be generated in the image quite often while performing the prior art method (for example, the image becomes reddish or bluish), and the white balance in the image becomes worse.